A group of compounds useful in photodynamic therapy, collectively designated green porphyrins, is disclosed in a series of patents including U.S. Pat. Nos. 5,283,255; 4,883,790; 4,920,143; 5,095,030; and 5,171,749, the disclosures of which are incorporated herein by reference. These green porphyrins are prepared using a Diels-Alder reaction with hematoporphyrin and optional rearrangement or reduction of the resulting product. A particularly preferred form of these green porphyrins, as outlined in the above-referenced patents, is designated a benzoporphyrin derivative in the monoacid form, or "BPD-MA". This drug is currently in clinical trials with respect to photodynamic treatment of various tumors and other conditions.
Photodynamic therapy rests on the assumption that the photoactive compounds administered, in this case the green porphyrins, are without physiological effect in the absence of light. However, when irradiated, the excited forms of the compounds exert local toxic effects. Therefore, for the treatment of tumors, for example, advantage has been taken of the tendency of these photoactive compounds to be retained in tumor tissue after clearance from normal tissue has been effected. It has also been found that local irradiation to areas of neovasculature is effective even before the compounds have been cleared from normal tissue.
It has now been found that the green porphyrins have immunomodulating activity and interfere with intercellular communication independent of their ability to behave as photoactive agents in PDT. The present invention takes advantage of this property, hitherto unexpected, of the green porphyrins.